1. Types of technological communications between operators.
In case of all complexity of CTS there are standard connections of the operators among themselves uniting them in the single scheme. Treat them: consecutive connection, parallel connection, consecutive and bypass (bypass) connection and recirculation connection. There is also a kind of the difficult connections uniting several types of elementary connections at the same time.
Consecutive connection:
Consecutive connection is the main connection of technological operators among themselves. At this connection all technological stream leaving the CTS previous element completely arrives on the subsequent CTS element, and each element passes a stream only once.
Parallel connection:
At parallel connection, the technological stream is divided into several streams which arrive on the CTS various elements, and each device passes a stream only once. The streams leaving elements can unite in one stream, and can leave separately.
Consecutive and bypass (bypass) connection:
At consecutive and bypass (bypass) connection passes through a number of consistently connected CTS elements only a part of a stream, and other part bypasses a part of devices, and then connects to a part of the stream which has passed through the CTS elements.
Recirculation connection:
Recirculation connection is characterized by existence of the reverse technological flow in system sequentially of connected elements which connects an output of one of the subsequent elements to an input of one of the previous elements. CTS with use of this communication are characterized by recirculation coefficient, i.e. the relation of a recirculating flow to summary (the coefficient is always less than unit).
It is necessary to consider that in case of synthesis and optimization of CTS usually it is required to consider rather large number of versions of the diagrams differing in technological topology. To reduce this quantity, and, therefore, helps to spare time and money along with an intuition of the developer, his ability to beforehand estimate effect which is possible for expecting in case of different types of connections between the CTS elements.
The stage of the reactors of ideal mixing (RIM) representing a row of sequentially connected reactors owing to change of a hydrodynamic situation will approach the reactor of ideal extrusion (RIE). Thus, changeover one RICE on a stage RICE gives the positive effect. Changeover of one RIV by a stage of RIV doesn't give any effect, however if length of RIV is required rather big, happens more expediently (from the point of view of more compact design of the equipment) to replace one big reactor with a stage of smaller reactors.
replacement one RICE on the RICE cascade, i.e. consistently connected devices (without change of the general time of contact), allows to reach bigger extent of transformation due to change of a hydrodynamic situation and to reduce the constructive size of each reactor. Replacement of one RIV by the RIV cascade allows to reduce the constructive size of each reactor only;
replacement of one RIV or RICE by a number in parallel of the working reactors does not reduce overall effectiveness, but reduces the constructive sizes in parallel of the working reactors;
parallel connection of the additional device allows to increase loading on raw materials at preservation of invariable extent of transformation or, perhaps, to reach higher extent of transformation (without change of speed of supply of raw materials) due to increase in time of stay;
consecutive connection apply when it is necessary to carry out chemical transformation into several stages for endo-or exothermic reactions (especially reversible) proceeding in adiabatic reactors since allows to maintain optimum temperature at each stage (catalytic the reactor, for example, oxidations of SO2 in SO3 or ammonia synthesis);
consecutive connection is applied when it is necessary to carry out technological process with allocation of any component after each stage (for example, in the multistage air compressor after each step of compression there is a cooling of gas and release of drop moisture);
parallel connection is applied when it is necessary to distribute optimum loading between in parallel the working lines differing on productivity, for example, owing to falling of activity of the catalyst, pollution of a heatexchange surface and so forth;
• parallel connection is applied when it is necessary to increase reliability of production and to provide a possibility of its work with the minimum performance without decrease in overall performance of the equipment (in case of need, parallel lines can be disconnected on economic purposes or for repair);
• in case of bypass connection owing to reduction of the flow going via the reactor time of stay in the reactor increases and extent of transformation of raw materials into products increases (in the reactor);
• bypass connection is applied when designing reactors to carrying out reversible exothermic reactions by mixture of a "hot" flow after the reactor with a "cold" bypass flow that allows to reach high extent of transformation and optimum temperatures and therefore high speeds of chemical reactions (catalytic the reactor, for example, oxidations of SO2 in SO3 or ammonia synthesis);
• recirculation is applied in cases when it is necessary to increase efficiency of use of raw materials and the equipment due to increase in time of stay in the recirculated devices without change of the sizes of the equipment and a hydrodynamic situation, i.e.;
• recirculation allows to reach the maximum use of raw materials (especially for reversible reactions) and to increase process speed due to increase in concentration of initial reagents which is reached in case of allocation of a target product on the line of recycling and return of initial reagents to process "head" (for example, an ammonia synthesis cycle);
• recirculation allows to reduce completeness of course of collateral chemical reactions by means of raw materials dilution by the reaction products arriving in process "head" through recycling.
As it was specified, data of heuristics belong to reactors, i.e. it is possible to constitute similar lists эвристик for other CTS elements. Besides, the list эвристик for reactors can be expanded for the account heuristics, which are a consequence stated above.
Test questions
1. Types of technological communications between operators.
2. What main technological operators, their features exist.
3. What auxiliary technological operators, their features exist.
Lecture No. 4. CTS properties.
Lecture purpose: studying of the CTS main properties.
Plan of a lecture:
1. CTS Emergency
2. Sensitivity of CTS.
3. Controllability of CTS.
4. Reliability of CTS.
5. Stability of CTS.
CTS represents set of technological operators – CTP interconnected by technological communications. As each CTP has own work characteristic, which is determined complexity of an element, consolidation of elements in CTS, will be followed by mutual imposing of work characteristics of elements. The situation will be aggravated in case of complication of technological communications between elements. Thus, thanks to consolidation of elements in system, it purchases new qualities, which aren't possessed by elements separately. The simplest example of imposing of characteristics of elements in case of their consolidation is provided to CTS in Fig. 1.5.
Fig. 1.5. Illustration of a work characteristic of CTS
In the drawing it is visible that work characteristics of the devices forming CTS have monotonous nature without extrema, however the work characteristic of CTS substantially differs from characteristics of its elements.
It is known that real productions contain many tens of technological devices connected by various types of connections and working as a unit. Thus, even in case of relative simplicity of work characteristics of devices, the work characteristic of CTS will be rather difficult, unpredictable and to depend on CTS topology. It should be noted that the work characteristic of CTS considerably can change even in case of an invariable set of elements, but in case of change of its topology (the CTS this property is called an emergency). Determination of a work characteristic of CTS is possible only as a result of calculations or industrial testing.
We will consider other CTS properties which need to be considered when designing new or reconstruction of the existing production, and also in case of operation of existing:
Sensitivity of CTS to external and internal indignations (impacts) is a capability of system to react to them, i.e. to change condition parameters. It is necessary that the system was insensitive to indignations;
Controllability of CTS is a property to achieve the objectives of management. Usually the purpose of management is release of the set product quantity of required quality. For ensuring required controllability, designing of CTS is made together with designing of a management system;
Reliability of system – property to keep working capacity during the set functioning time. This problem is solved at a design stage so that even in case of failure of some part of the service equipment or a part of a management system, the system kept the working capacity;
Stability – a capability of CTS to return to initial steady state after elimination of the indignations, which caused a system exit from this condition.
Control questions
1. Give definition and explain an essence of CTS properties (an emergency, sensitivity, controllability, reliability, stability).
Theme 2. The TASKS SOLVED WHEN DESIGNING CTS.
Lecture No. 5. The tasks solved when designing CTS
Purpose: studying of the main objectives when designing CTS
Plan of a lecture:
1. Task of synthesis of CTS
2. Tasks of the analysis of CTS
3. Task of calculation of CTS
4. Task of optimization of CTS
Before to start a material statement, it is necessary to determine that designing belongs to a comprehensive concept. In fact, designing designates creation of the project, i.e. plan of future changes. Thus, under this concept not only creation of the new productions and reconstruction existing, and also upgrade of the operating productions since any changes on production shall be followed by creation of the project documentation regardless of whether there is a replacement of a part of the technological scheme or installation of the additional line of the pipeline gets. With respect thereto, the concept the project will have a number of versions, requirements to each of which are accurately determined in the corresponding regulating documentation.
Each CTS project shall contain:
1. Technological topology of CTS (technological topology call nature and an order of connection of separate devices to the technological scheme);
2. The ranges of changes of values of entrance variables which physical parameters of entrance flows of raw materials, and also environment parameters influencing process of functioning of CTS are;
3. Ranges of changes of values of the CTS technological parameters (extent of transformation, extent of separation of components, constants of speeds of chemical reactions, coefficients warm and mass transfers, etc.);
4. CTS constructional parameters (sizes of devices, heights of layers of a nozzle, etc.);
5. Recommended parameters of a technological operating mode of the CTS elements (temperature, pressure, catalyst types, etc.);
6. Parameters of the technological flows ensuring functioning of CTS in the set mode (temperatures, pressure, expenses, structure of flows, etc.).
To receive the parameters stated above it is necessary to solve a number of problems of synthesis of CTS, the analysis of its structure, calculation and optimization.
The task of synthesis of CTS is generally formulated as follows:
Elements of which the system, raw materials and target products can be constructed are known. In case of the solution of a task of synthesis it is required to develop the structure of CTS required for implementation of engineering procedure i.e. it is necessary to choose elements from among available; to establish connection between them; to determine design and technological data of the CTS elements.
Usually the task of synthesis is multiple, i.e. the same values of output parameters can be provided in case of various structure of system and the different modes of functioning of elements. It should be noted that the task of synthesis has features for designing of new production (CTS) and for reconstruction of existing. The essence of differences is that during creation of new CTS usually there are many opportunities of the choice of elements and communications between them, and in case of reconstruction of CTS it is required to keep everything or a part of its elements, and also all or a part of communications between elements.
Tasks of the analysis of CTS are subdivided into the analysis of structure of CTS and the analysis of quality of functioning of CTS.
The main objective of the analysis of structure of CTS consists in detection of its structural features and finding of the optimum sequence of calculation of its elements, and the purpose of the analysis of quality of functioning of CTS – receipt of quantitative estimates of its main properties: sensitivity, reliability, stability, etc.
The task of calculation of CTS consists in receipt of quantity characteristics both the modes of functioning of the CTS elements, and all system.
The task of optimization of CTS is complex since it includes both optimization of structure, and optimization of the modes of functioning of elements. A main objective of optimization of CTS is providing the highest technical and economic rates.
In conclusion it should be noted that between tasks of synthesis, the analysis, calculation and optimization there is an interrelation since during creation new or reconstruction of the existing production at first synthesis of several alternative options of CTS is carried out, it is analyzed their technical and economic indicators, and then search of an optimal variant is run.
Test questions.
1. List the main objectives when designing CTS.
2. Explain the purposes of tasks and communication between them.
Theme 3. SYNTHESIS of CTS
Lectures No. 6 - 8. Main methods of synthesis of CTS.
Lecture purpose: Studying of the main methods of synthesis of CTS
Plan of a lecture:
1. Purpose of a task of synthesis of CTS.
2. Synthesis methods.
3. Technological restrictions in case of the solution of a task.
When designing new or reconstruction of the existing production, one of the main tasks is synthesis of option of CTS allowing to reach high technical and economic rates. In a general view the task of synthesis of CTS is formulated as follows:
It is known: structure and parameters of raw flows; structure and parameters of productional flows; indicator of an optimality criterion of functioning of CTS; restrictions for parameters of functioning of the CTS elements.
It is necessary to determine: structure of CTS (the devices entering CTS); structure of CTS (communication between devices); design data of devices CTS; current technological parameters of work of CTS; the parameters of management of CTS satisfying to optimum parameters of functioning of CTS.
In case of the solution of a task of synthesis of CTS, the way of carrying out process (chemism), and only shall be originally determined then becomes possible to make synthesis of structure of CTS, determination of parameters of work of its elements and parameters of the flows connecting these elements. Because the task of synthesis is a complex multiple challenge, its decision is possible only when using a certain methodology and the corresponding approaches.
The method based on the principles of search of options of topology of CTS, parameters of functioning of elements, etc. can be the easiest way of synthesis. However, in connection with complexity of CTS and diversity of the solution of separate tasks of synthesis (mutual connection of reactors, heat exchangers, etc.) this method will require a large number of the additional information and time that can be insufficiently effective. For example, it is well known that spontaneously warmly to be transferred only from a hot flow to cold, therefore, the scheme assuming the return can be not considered. However, in case of simple search of various options, parameters of functioning of elements can be determined only after synthesis of topology of CTS and creation of its mathematical model necessary for calculation, and the calculation. Therefore, in this case, even impracticable options will require consideration, and, therefore, additional costs.
For decrease in quantity of the considered options usually carry out decomposition of a task of synthesis of CTS on a number of subtasks or levels (a decompositional method of synthesis of CTS). The example of such decomposition on seven levels is provided in Fig. 3.1. When using simpler – two-level decomposition, at the top level will come synthesis of CTS from subsystems (chemical interaction, separation, mixture and so forth) and to be determined parameter values of the flows connecting these subsystems. At the lower level synthesis of subsystems will be made and to be determined parameter values of the flows connecting the devices entering these subsystems. In this case, if the version of any synthesized scheme in case of its calculation is impracticable, costs for synthesis, the analysis, modeling and calculation of option of CTS will be less. However even the task of synthesis of subsystems is rather difficult and requires additional decomposition or application of other methods of synthesis.
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1. Choice of routes and conditions of carrying out reactions
2. Definition of optimum systems of chemical reactors
3. Definition of optimum systems of division of mixes
4. Choice of auxiliary subsystems
5. Definition of optimum systems of heat exchangers
6. Qualitative analysis of reliability of CTS
7. Analysis of the CTS dynamic properties
Fig. 3.1. Order multi-level decomposition of a task of synthesis of CTS
It is possible to refer the heuristic principle of synthesis of CTS which consists in mathematical formalization of the intuitive heuristic method which is widely used by designers to the principles allowing to solve more effectively a problem of synthesis of CTS a decomposition method, and, allowing highly qualified specialists to choose intuitively the most successful ways of solving the problem without complete search of all possible alternative options. When using this method decision making happens without reasons it by means of proofs. However this method of decision making doesn't reduce its value as it uses intuitive factors and rules, i.e. the generalizing knowledge and wide practical experience of highly qualified specialists.
We will consider some heuristics, applied in case of development of technological schemes of a number of functional subsystems of chemical productions. For example, for the choice of the optimum technological scheme of separation of multicomponent mixes from a set of alternative options it is possible to use the heuristics following:
a) the choice of option with consecutive allocation of target products in the form of easy products of elements of a subsystem;
b) the choice of option, in which the relation of quantities of the upper and lower products in each element of a subsystem most close to 1;
c) the choice of option in which separation of components is performed as reduction of distinctions in values of relative volatilities of the divided key components;
d) the rectifying columns requiring the greatest costs for separation owing to close relative volatilities of key components or high requirements to purity of products shall be placed at the end of the scheme of separation;
e) the choice of the option which is characterized by the minimum size of the given costs for implementation of this engineering procedure in a subsystem element, etc.
In case of development of optimum technological schemes of thermal subsystems
(systems of heat exchangers) the heuristics following can be used:
a) couple of flows for which the amount of the transferred heat is maximum are chosen;
b) couple of flows for which the set final temperatures of flows aren't reached are chosen, and the cost of use of auxiliary heat carriers for bringing temperature of these flows to the set final values is minimum;
c) couple of flows which heating/chilling cost auxiliary warm / coolant is maximum are chosen;
d) couple of flows for which the cost of heat exchange is minimum, etc. are chosen.
In case of use of the heuristic principle of synthesis success in the basic depends on that, heuristic conditions are how close to conditions of achievement of an optimality of the considered CTS subsystem, and also from an order of application of heuristic conditions, type of a synthesizable subsystem, its complexity, parameters of flows and so forth. For determination of this order of application эвристик use weight functions separate эвристик.
As an example, we will review/7/example of synthesis of the system of heat exchangers providing heating and chilling of technological flows to the set temperatures provided in literature.
As well as for any technological scheme in an example the following restrictions are used:
• the technological scheme shall use as much as possible energy of flows ("cold" flows shall heat up whenever possible "hot" flows);
• technological flows can't be divided, however if separation of a technological flow is necessary, then the divided parts of a flow shall be considered as separate flows;
• the synthesizable thermal scheme shall have the minimum costs for implementation of the set transaction of heat exchange between flows;
• if for heating/chilling of flows it is impossible or unprofitable to use other flows, external heat carriers can be used: saturated steam with pressure of 31,6 kgfs/cm2 and the cooling water with a temperature of 38OC, and water it is impossible to heat higher than 82OC;
• in case of heat exchange between technological flows, chilling their water and heating steam, respectively, reaches the following coefficients of a heat transfer: 852, 852, 1136 W / м2;
• in case of heat exchange between technological flows, chilling by their water and heating steam, respectively, the minimum rapprochement of temperatures of the processed temperatures in the heat exchanger constitutes 11, 11 and 13OC.
Initial parameters of technological flows are provided in Table 3.1.
Table 3.1.
Parameters of technological flows
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№ of flow
Expense, т/h
Initial Т, 0С
Finit Т, 0С
Thermal capacity,, kcal/kg
1
20
100
430
0,80
2
40
440
150
0,70
3
35
520
300
0,68
4
36
180
350
0,91
5
31
200
400
0,85
6
32
350
410
0,62
7
42
390
150
0,80
According to methodology of use of the heuristic principle, the order of synthesis of the thermal scheme (CTS) will be following:
All set of flows is divided into subsets of the flows, which are subject to heating (a flow 1, 4, 5 and 6) and to chilling (a flow 2, 3 and 7). The weight coefficients different 0,5 are appropriated to all heuristics (will be used described above heuristics);
Search of flows of both subsets determines a possibility of implementation of transactions of heat exchange (i.e. at first a flow 1 with flows 2, 3, 7, then a flow 4 with flows 2, 3, 7, etc.). Couples of flows for which heat exchange is possible are entered in the table of couples of processed flows;
By means of the heuristics chosen taking into account weight coefficients one couple gets out of the table of couples of processed flows and for it calculation of the heat exchanger is made, i.e. final temperatures of flows are calculated;
If the calculated final temperatures of flows correspond to the set final temperatures, then these flows are struck off lists. Otherwise, the flows having the calculated final temperatures are entered in tables as the remained raw flows;
Points 2-5 repeat until all couples of processed flows are exhausted;
The remained flows not reached final temperatures are exposed to heating/chilling by auxiliary flows. The given costs for implementation of the synthesized scheme are calculated;
Calculated, by means of any technique, the size of the given costs is compared to the minimum value received earlier (the original cost of system of heat exchangers is calculated for system in which heating and chilling is carried out only by auxiliary water flows and couple). If the received decision turns out more economic, then the weight coefficients used эвристик increase, otherwise – decrease. If the weight coefficient of heuristics is equal to zero, then this heuristics isn't used further.
Process of synthesis of CTS is conducted until present value of costs falls. In case of stabilization of present value of costs on some minimum value, calculations stop. The synthesized operator scheme of system of heat exchange (for this example) is provided in Fig. 3.2.
Fig. 3.2. The operator scheme of the synthesized system of heat exchange
Decrease in the given costs in the course of synthesis of the thermal scheme is provided in Fig. 3.3.
Fig. 3.3. Change of the given costs in the course of synthesis of thermal schemes.
Apparently from drawings, the synthesized thermal scheme has the minimum given costs and consists of eight heat exchangers, five of which give warmth from the cooled flows to heating up, and only in three heat exchangers external coolant moves.
The considered principles of synthesis of CTS rather widely are applied in case of synthesis of new productions, however in case of reconstruction of the existing productions, use of these principles will lead to consideration of excessive quantity of options and can be insufficiently effective. For the purposes of upgrade of the existing technological scheme, as well as for synthesis of new CTS the evolutionary principle of synthesis can be used.
The methodological basis of the evolutionary principle of synthesis of CTS consists in consecutive modification of hardware registration and correction of structure of technological connections of some initial option of CTS with use of methods of heuristics and optimization. Otherwise, when using the evolutionary principle of synthesis of CTS, at first the initial option of technological topology of CTS, for example, by means of the heuristic principle of synthesis is created. By means of analysis methods for this option there is a "narrow" place of CTS, the optimality criterion is determined, and the corresponding modification of hardware registration and structure of technological communications is made. After the specified modification calculation of an optimality criterion and new search of the "narrow" place of CTS is made again. Process of modification of CTS is made until required value of an optimality criterion is reached. Thus, logically, this process consists of consecutive iterative alternation of stages of synthesis, the analysis, optimization and modification of some originally set technology solution of a task of synthesis of CTS or the existing technological scheme.
Thus, practical implementation of the evolutionary principle of synthesis is connected with need of use of the following types эвристик: heuristics generalizing practical experience (the least effective elements or bottlenecks allowing to allocate in initial option of technological topology of CTS); intuitive heuristics (the possible options of modification or enhancement of bottlenecks of CTS allowing to determine); heuristics, based on knowledge of highly qualified specialists (the "joinings" of the modified CTS element with an unmodified part of CTS providing an opportunity).
In conclusion, it should be noted that, unfortunately, use of the evolutionary principle of synthesis of CTS allows to receive local optimum results with the greatest efficiency that is caused by the fact that the result of the decision is considerably determined by the main concepts accepted at the first stage in case of development of initial option of technological topology of CTS.
Test questions
1. Formulate the purposes of a task of synthesis of CTS.
2. Synthesis methods.
3. The technological restrictions considered in case of the solution of a task of synthesis.
THEME 4. MAIN METHODS OF CALCULATION OF XTC.
Lecture No. 9 - 11. Calculation of CTS
Lecture purpose: studying of methods of calculation of CTS
Plan of a lecture:
1. Integrated method of calculation.
2. Decompositional method of calculation.
3. Iterative method of calculation.
The main objective of calculation of CTS at the set parameters of functioning of technological operators, is finding of parameters of a condition of the streams connecting the specified technological operators. Methods of the solution of this task usually divide into two groups: integrated (they still are called composite) and decompositional. In turn, depending on the principles of creation of models, each of methods has various ways of calculations.